Process of preparing cellulose for its fibrous esterification



Patented Oct. 15, 1935 UNITED STATES PATENT OFFICE PROCESS OF PREPARING C'ELLULOSE FOR ITS FIBROUS ESTERIFJICATION New York No Drawing. Application May 19, 1933, Serial No. 671,898

7 Claims.

' The present invention relates to the pretreatment of cellulose prior to its fibrous esterification with a mixture of a fatty acid and a hydrocarbon non-solvent with or without a catalyst.

There are two principal types of processes for the preparation of the organic acid esters of cel- 1ulose,'namely (1) dope processes in which the ester formed, enters into solution in the esterification bath and (2) fibrous processes in which the esterification bath is non-solvent of the cellulose ester formed. Dope esterification processes are ordinarily carried out by pretreating cellulose with sumcient acetic acid to thoroughly penetrate and act upon the cellulose. The presence of a catalyst in the pretreatment bath is usually desired. The acetic acid is carried over into the esterification bath proper, in fact the esterification is usually carried out by adding the acid anhydride to the pretreatment mass after that step has been completed. As solution of the cellulose ester formed is desired the presence of the acetic acid is quite advantageous as it'acts as the solvent and diffusing agent in the bath.

Obviously in the second type of esterification process, namely fibrous, the presence of a considerable amount of acetic acid such as would be present after the ordinary pretreatment for dope esterification would be undesirable due to its solvent tendencies, which would necessitate the use of a rather large amount of non-solvent.- To overcome this handicap, pressing or draining, in some manner, of the cotton has been resorted to and by reducing the amount of acetic acid present, its effect is considerably reduced. However the removal of acid from the cotton is usually somewhat difiicult and costly and at best there still remains a considerable amount of acid adhering to the cellulose fiber.

One object of our invention is to provide a process for pretreating cellulose which is adapted for use with a fibrous process of esterifying cellulose. Another object of our invention is to provide a process for pretreating cellulose in which the cellulose is satisfactorily activated or made ready for esterification and yet there is no necessity of draining, pressing or the like after the pretreatment. 7

We have found that if cellulose is pretreated with a lower fatty acid and a hydrocarbon nonsolvent, that cellulose is eminently suited for esterification in a fibrous process. We have found that cellulose may be pretreated very efliciently by this method with only a small'amount of the organic acid so that the solvent effect thereof in the esterification bath is reduced to a minimum, due to the fact that the hydrocarbon aids the distribution and penetration of the pretreating acid throughout the cellulose. We have found that the thus pretreated cellulose necessitates a smaller amount of non-solvent in the esterification than does a cellulose which has been pretreated in the customary manner, namely with acetic acid and a catalyst. We have found that our pretreatment efiectively activates cellulose for esterification purposes whether or 10 not a catalyst is employed in the pretreatment bath and in fact the pretreatment of the cellulose in the absence of the catalyst is preferred.

Our invention comprises the step of pretreating the cellulose with a solution of an organic acid 15 in a hydrocarbon diluent, which diluent will act as a non-solvent of the cellulose ester formed in the subsequent esterification bath. The follow-- ing examples illustrate fibrous processes of estere ifying cellulose which embody our invention:

Erample I 25 lbs. of cellulose was treated with a solution of 25 lbs. of glacial acetic acid and 0.4 lb. of 95% sulfuric acid in 24 lbs. of a petroleum hydrocarbon having a boiling range of approximately -120 C. for about 16 hours at approximately 25 C. The cellulose was then esterified by adding to they mass a mixture of 30 lbs. of acetic anhydride, 35 lbs. of propionic anhydride and 56 lbs. of petroleumhydrocarbon similar to that employed in the pretreatment. The esterification was allowed to proceed for 24. hours at 40 C. The product, which was cellulose acetate propionate, was found to give a clear, brilliant dope 35 in ethylene chloride or in ethylene chloridealcohol.

Emample II Example III 25 lbs. of cotton linters was pretreated for 16 hours at room temperature with solution of 25 lbs.

of glacial acetic. acid in 20 lbs. of a low boiling 5 petroleum hydrocarbon. Esterification was then induced by adding a mixture comprising 33 lbs. of propionic anhydride, 33 lbs. of 95% acetic an hydride and 2 lbs. of a catalyst consisting of 3 parts of phosphoric-acid and 1 part of sulfuric acid by volume. Enough petroleum hydrocarbon was then added so that the whole mass had a volume of about 18 gallons. The temperature was 20 C. at the start and was allowed to rise to 40 C. over a period of 2 hours and was there maintained for hours, at the end of which time the reaction was complete. The product was washed With hot water to remove the non-solvent and then with tap water to remove any acid remaining. It was dried at 55-60 C. The ester was dissolved in a mixture of ethylene chlorideethyl alcohol (95:5) and was coated out in the form of a skin which exhibited good flexibility.

Example IV v 25 lbs. of cotton linters was treated with 25 lbs. of acetic acid and 20lbs. of a low boiling petroleum hydrocarbon for 16 hrs. at room temperature. Esterification was then brought about by adding thereto a mixture of 40 lbs. of butyric anhydride, parts of acetic anhydride, 2 lbs. of a catalyst consisting of 1 part by volume of sulfuric acid and 3 parts by volume of phosphoricacid and 68 lbs. of low boiling petroleum hydrocarbon at 20 C. The temperature was allowed to rise to C. over a period of two hours and the bath was maintained at that temperature for 48 hours to assure complete esterification. The ester was then washed with hot water to remove the non- I solvent and then with cold water untilthe fibers were free of acid. The product was dried at 50-60 C. The ester was coated out from its solution in ethylene chloride-alcohol (95:5) to form skins or sheets which were found to be as flexible or more so, without the addition of plasticizer, as sheets of the ordinary hydrolyzed cellulose acetate, containing15% by weight of triphenyl phosphate.

Processes were carried out resembling the above except that the ratios of butyric to -acetic anhydride were varied and in each case an excellent product was obtained.

Example V 25 lbs. of cotton linters was pretreated with 5 lbs. of acetic acid dissolved in lbs. of Stoddard solvent for 24 hours at room temperature. The pretreated cotton was then esterified by adding thereto 70 lbs. of acetic acid, 34 lbs; of propionic acid, 6'7 lbs. of acetic anhydride, 50 lbs. of propionic anhydride, 140 lbs. of Stoddard solvent, 30 lbs. of trichlorethylene and about lb. of sulfuric acid. The whole was maintained at 40 C. and the esterification was completed in 24 hours. The ester formed was separated from the reaction mixture in the usual manner and was found to be soluble in ethylene chloride-alcohol"(95;5)

The proportions of fatty acid to Stoddard solvent in the pretreatment have been varied as follows and samples of good solubility have been obtained: 1

Due to the fact that the proportion-by volume of the Stoddard solvent in the pretreatment may be varied considerably and that the amount of acid in the pretreating mixture may be small, this pretreatment is eminently adapted to fibrous esterification processes involving reuse of the spent esterification liquors, such as are disclosed and claimed in Hopkinson and .Fordyce application Seriol No. 682,726, filed July 28, 1933. We have found that in this pretreatment a bath containing as low as 10% of fatty acid based on the weight of the cellulose (cotton linters) has been employed successfully.

Example VI tion mass, washed until acid free and was dried at 50-60 C. It was soluble in ethylene chlorideethyl alcohol (95:5).

Our invention also admits of various modifications by the individual operator. For instance, instead of employing acetic acid in the pretreatment, other acids such as propionic and/ or butyric or the mixture of either or both with acetic acid may be employed as the active acid constituent of the pretreatment bath. Thus it may be seen that our invention is not alone directed to the preparation of cellulose acetate propionate and of cellulose acetate, but also to the preparation of the simple higher esters, such as cellulose propionate, cellulose butyrate, as well as mixed esters, such as cellulose acetate butyrate, cellulose propionate butyrate and cellulose acetate propionate butyrate.

Various hydrocarbon non-solvents or diluents may be employed in our inventions, such as the aliphatic hydrocarbons and the cyclic hydrocarbons, both saturatedand. unsaturated. Of the aliphatic hydrocarbons which are suitable for use as non-solvents are included ligroin, kerosene, gasoline, naphtha, petroleum spirits and Stoddard solvent. Stoddard solvent is a commonly known distillate described in Bureau of Standards Bulletin C. S. 3-28 (1929). The use of certain members of this class of hydrocarbons as nonsolvents in fibrous esterification processes is disclosed in application Serial No. 671,900 of even date of Minsk, Kenyon and Gray. The petroleum hydrocarbons which are especially suitable as nonsolvents are those containing substantial quantities of hexane or heptane. Of the aromatic hydrocarbons, benzene, toluene, Xylene or cymene V are eminently suitable for use as a non-solvent in a fibrous esterification process, while cyclohexane is an example of a saturated cyclic hydrocarbon which. is suitable for use as a non-solvent.

We claim as our invention:

, 1. In the preparation of an organic acid ester of cellulose in fibrous form, the step which comprises pretreating the cellulose with a mixture of a lower fatty acid and a low boiling aliphatic hydrocarbon diluent at a temperature of approximately 20-25 C. preliminary to its esterification.

- 2. In the preparation of organic acid esters of cellulose'in fibrous form, the step which comprises pretreating the cellulose with a mixture of a lower fatty acid and a low-boiling petroleum distillate at a temperature of approximately 20-25 C. preliminary to its esterification.

3. In the fibrous preparation of an organic acid ester of cellulose, the step which comprises pretreating the cellulose with a mixture of acetic acid and a low-boiling petroleum distillate at a temperature of approximately 20-25 C. preliminary to its fibrous esterification.

4. A process for preparing an organic acid ester of cellulose in fibrous form which comprises pretreating the cellulose with a mixture comprising a lower fatty acid and a low boiling aliphatic hydrocarbon diluent at a temperature of approximately 20-25 C. and then adding an esterification inducing material thereto.

5. A process for preparing an organic acid ester of cellulose in fibrous form which comprises pretreating the cellulose with a mixture comprising a lower fatty acid and a low boiling aliphatic hydrocarbon diluent at a temperature of approximately 20-25 C. and then adding an esterifying material comprising a fatty acid anhydride thereto. v

6. A process for the preparation of a cellulose acetate propionate in fibrous form which comprises pretreating cellulose with a mixture comprising acetic acid and a low boiling aliphatic hydrocarbon diluent at a temperature of approximately 20-25 C. and then adding'an esterifying material containing propionyl groups thereto.

'7. In the preparation of an organic acid ester of cellulose in fibrous form, the step which comprises pretreating the cellulose with a mixture comprising a lower fatty acid and a petroleum hydrocarbon having a boiling range of 60-120 C.,

at a temperature of approximately 20-25 C. preliminary to its esterification.

EDWARD C. YACKEL. WILLIAM O. KENYON. 

